HgFET: A new characterization tool for SOI silicon film properties

A new version of the pseudo-FET, called the HgFET, is described in which a combination of broad area Hg electrodes coupled with special surface treatment are used to overcome the limitations of point contacts. The device consists of a 20 mil diameter Hg mesa which act as the drain, completely surrounded by a ring of Hg acting as the source. This ring-dot configuration completely isolates the device from the rest of the wafer. Prior to contacting the Si surface with the Hg electrodes, the surface is treated with HF to remove any native or other oxide and `passivate' the surface, reducing the surface state density to a low level and introducing a layer of excess charge on the surface which influences the device characteristics but decays away in 30 to 60 minutes.